Prevention and remedy of common defects in heat treatment process of automobile piston pin parts

1.The concentration of carburized layer is too high

Characteristics of heat treatment defects:

There are massive carbides or network carbides distributed along grain boundaries in the surface structure of carburized layer.

Causes of heat treatment defects:

1) During carburizing, the carbon potential of furnace gas in the furnace is too high, such as excessive oil drop;

2) The diffusion stage of carburized parts is insufficient, the diffusion temperature is low or the diffusion time is short.

Preventive measures for heat treatment defects:

1) Properly control the atmosphere carbon potential in the carburizing furnace and adjust the drop amount of carburizing agent;

2) After carburizing, the diffusion time shall be appropriately prolonged.

Remedies for heat treatment defects:

1) Allow diffusion at 900 ~ 920 ° C to eliminate excessive carbides;

2) If only the fine network carbide distributed along the grain boundary exists, it can be eliminated in reheating quenching.

2.The concentration of carburized layer is too low

Characteristics of heat treatment defects:

1) The microstructure of carburized layer in annealed state is hypoeutectoid;

2) The hardness of parts after quenching is not enough.

Causes of heat treatment defects:

1) The carbon potential of furnace gas in furnace is too low during carburizing;

2) Poor circulation of furnace gas in furnace;

3) Excessive charging of parts.

Preventive measures for heat treatment defects:

1) Strictly control the carbon potential of furnace gas within the range of process requirements;

2) Improve the furnace gas circulation system;

3) Reduce furnace loading;

4) During charging, the clearance between parts shall be as uniform as possible, and iron shall be used if necessary.

Remedies for heat treatment defects:

When the carburized layer does not exceed the upper limit of technical requirements, it is allowed to re carburize for supplementary infiltration.

3.Carburized layer out of tolerance

Characteristics of heat treatment defects:

The depth of carburized layer is too deep or too shallow.

Causes of heat treatment defects:

1) High or low carburizing temperature;

2) Carburizing time is too long or too short.

Preventive measures for heat treatment defects:

1) Check the furnace temperature frequently;

2) Strictly control carburizing time.

Remedies for heat treatment defects:

1) The carburized layer is too thick and scrapped;

2) If the carburized layer is too shallow, supplementary infiltration is allowed.

4.Uneven carburizing layer depth

Characteristics of heat treatment defects:

When observed along the transverse incision, the depth and thickness of carburized layer are uneven.

Causes of heat treatment defects:

There is dirt or dust on the part surface, or the furnace is poorly charged, and there is mutual superposition between the part surfaces.

Remedies for heat treatment defects:

Under the condition of ensuring that the carburizing depth does not exceed the difference, it is allowed to reduce the temperature for supplementary infiltration.

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